It is well known in the art that the mineralization of dental deposits and the subsequent formation of calculus (hydroxyapatite deposit) occurs via a homogenous nucleation (an increase in Ca.sup.++ ions or orthophosphate ions) and/or via heterogeneous nucleation (specific salivary and bacterial proteins). However, in either case, salivary Ca.sup.+2 is added to the salivary orthophosphate leading to hydroxyapatite (HAP) formation. The formation of HAP in vitro occurs in two distinct steps:
1. When Ca.sup.+2 is added to orthophosphate at constant pH (7.4, by pH stat), there is rapid consumption of base as a function of time, that is, 1-4 minutes.
2. Then the base consumption diminishes for about 15-20 minutes after which the second uptake of base occurs. A delay in the time of the second rapid consumption of base, or a total absence of a second rapid consumption suggests an interference with the crystal growth of HAP. Accordingly, compounds which interfere with crystal growth of HAP are effective anticalculus agents.
It is also known that the magnesium ion, Mg.sup.+2, reduces the overall rate of crystallization by stabilizing the precursor (amorphous deposit) formed intially with Ca.sup.+2 and orthophosphate, as disclosed in "Growth of Calcium Phosphates on Hydroxyapatite Crystals: The Effect of Magnesium, Arch. Oral Biol, 20:803, 1975. The amorphous deposits are readily removable while the crystalline phase is difficult to remove. However, the residence time of externally introduced Mg.sup.+2 ion in the oral cavity is low. Saliva also has an extremely low Mg.sup.+2 content (J. Periodontal Res. 9:211-221, 1974).
It has now been found that the efficacy of the magnesium ions can be improved by combining magnesium with a polycarboxylate selected from the group consisting of the maleic acid copolymers, the sulfoacrylic oligomers and the tricarboxy-oxa-butanol or pentanol to form a complex therewith. Since there are at least two carboxyl groups per mole of polycarboxyl-containing compound (e.g. two carboxyl groups per mole of maleic acid), one carboxyl is available to react with Mg.sup.+2 (2/3 ionized) and there are enough free COO.sup.- to react with the tooth enamel.